This disclosure relates in general to skew correction and, but not by way of limitation, to skew correction for scanned documents amongst other things.
When digitizing document pages, whether from paper, books, microfilm, or other sources, it is often the case that the resulting image contains some amount of skew. The skew in a digitized document may result from the scanning process or may be an affect from the original document source. In some cases skew can be found in documents digitized or needing to be digitized for the purpose of optical character recognition (OCR). Skew can be defined as the angle between a reference line, such as a horizontal line, and an element of an image that should be parallel with the reference line.
To correct for skew, the magnitude and the direction of the skew must be known in order to deskew an image. A number of automatic techniques have been developed to correct for skew. These techniques, however, are not perfect. Some images with skew are not deskewed and other non-skewed images become skewed as a result of an automatic deskew algorithm. Such skewed images may need to be deskewed manually.
Manual deskewing can be difficult, time consuming and frustrating. In some cases, the operator may manually rotate an image using a pointing device such as a mouse. In other cases, the user may be required to enter a skew-angle or a rotation angle—a concept not easily understood by many users. This may result in a potentially laborious two step process: to estimate or calculate a rotation angle and then to enter the rotation angle. Once the angle is entered into a computer system, the image is rotated accordingly. Often an estimated rotation angle is incorrect, requiring the user to enter additional estimated rotation angles until the user is satisfied with the new orientation of the image. If large numbers of images require deskewing, a two-step process such as the one described can be time consuming and inaccurate. It may take multiple tries for a user to successfully arrive at the correct (or approximately correct) skew-angle and properly deskew an image.
Accordingly, there is a need in the art for improved user-coordinated deskewing techniques.